Isomerization unit with integrated feed and product separation facilities

Abstract

A combination isomerization-reforming process provides additional liquid volume yields of gasoline without significant increase in utilities expense by recycling the isomerization zone effluent to an extended feed fractionation zone from which an isomerization product is also withdrawn. The feed fractionation zone receives a C 5 -plus boiling range naphtha feed. The fractionation zone provides a relatively heavy bottoms stream for a reformer feed and a relatively lighter sidecut stream for feed to an isomerization zone. Effluent from the isomerization zone is recycled to the feed fractionation zone at a midfractionation entry point. A net overhead stream withdrawn from the feed fractionation zone and containing principally C 6 isoparaffins and lighter boiling hydrocarbons provides a relatively high octane blending component. The fractionation zone overhead stream may be combined with effluent from the reforming zone to obtain a gasoline product, at high liquid volume yield, having sufficient octane for unleaded motor fuel use.

What is claimed is: 
     
       1. A process for upgrading C 5  and C 6  components of a C 5  and higher boiling feed stream into higher octane components, said process comprising: (a) passing said feed stream into a fractionation zone and separating said feed stream into higher and lower boiling components;   (b) withdrawing a relatively heavy stream comprising C 7  -plus hydrocarbons from said fractionation zone;   (c) withdrawing an intermediate stream, rich in normal hexane and lower boiling range hydrocarbons from said fractionation zone, and contacting said intermediate stream, in an isomerization zone, with an isomerization catalyst at isomerization conditions;   (d) returning a recycle stream comprising at least a portion of the effluent stream from said isomerization zone to said fractionation zone; and   (e) withdrawing a relatively light stream from said fractionation zone, said relatively light stream comprising C 6  isoparaffins and lower boiling hydrocarbons.   
     
     
       2. The process of claim 1 wherein said feed stream inlet, intermediate stream outlet, and recycle stream inlet have progressively higher locations on said fractionation zone. 
     
     
       3. The process of claim 1 wherein said relatively light stream, intermediate stream, and relatively heavy stream are the overhead, sidecut, and bottoms streams, respectively of the fractionation zone. 
     
     
       4. The process of claim 1 wherein said feedstream comprises a C 5  -plus naphtha boiling range hydrocarbon stream having an end boiling point of 205° C. 
     
     
       5. The process of claim 1 wherein the isomerization zone effluent is stabilized by removal of C 3  -minus hydrocarbons. 
     
     
       6. The process of claim 1 wherein said fractionation zone includes a first fractionation column from which said intermediate stream orignates and a second fractionation column that receives said recycle stream. 
     
     
       7. The process of claim 4 wherein said relatively heavy stream contacts a reforming catalyst at reforming conditions in a reforming zone. 
     
     
       8. The process of claim 7 wherein the effluent from said reforming zone is combined with said relatively light stream to form a gasoline product stream. 
     
     
       9. A process for upgrading a C 5  naphtha boiling range hydrocarbon feedstream, said process comprising: (a) passing said feedstream into a fractionation zone;   (b) withdrawing a bottoms stream comprising C 7  -plus hydrocarbons from said fractionation zone and passing said bottoms stream to a reforming zone;   (c) contacting said bottoms stream, in a reforming zone, with a reforming catalyst at reforming conditions to produce a reforming product stream;   (d) withdrawing a sidecut stream comprising normal hexane and lower boiling hydrocarbons from said fractionation zone and passing said sidecut to an isomerization zone;   (e) contacting said sidecut with an isomerization catalyst at isomerization conditions in said isomerization zone to produce an isomerization zone effluent stream rich in C 6  and lower boiling hydrocarbons;   (f) passing at least a portion of said isomerization effluent stream to the fractionation zone as a recycle stream; and   (g) withdrawing an overhead stream comprising C 6  isoparaffins and lower boiling hydrocarbons from said fractionation zone.   
     
     
       10. The process of claim 9 wherein the fractionation zone comprises trayed columns and the feed entry point, sidecut withdrawal point, and recycle entry point are at progressively higher tray locations. 
     
     
       11. The process of claim 10 wherein at least a portion of said overhead stream and said reformate product stream are combined to form a gasoline product stream. 
     
     
       12. The process of claim 11 wherein said sidecut stream consists essentially of C 5  and C 6  hydrocarbons. 
     
     
       13. The process of claim 12 wherein said isomerization zone effluent is charged to a stabilization zone for the removal of C 3  and lighter hydrocarbons before entering the fractionation column. 
     
     
       14. The process of claim 13 wherein said fractionation zone comprises at least two fractionation columns. 
     
     
       15. The process of claim 14 wherein said recycle stream enters a first column in said fractionation zone and said sidecut stream emanates from a second fractionation column in said fractionation zone. 
     
     
       16. The process of claim 9 wherein said fractionation zone is operated at a temperature and pressure to provide a cut point between the recycle stream and the sidecut stream at the boiling point of methyl pentane.